Pre-heat the oven to 200°C, 400°F, Gas Mark 6.
Par-boil the parsnips for 5 minutes, drain and place in a large roasting dish with the onions and peppers. Drizzle with the olive oil and sprinkle over the packet contents.
Cook in the oven for 35-40 minutes, or until the parsnips are tender.
Meanwhile, place the pastry onto a greased baking sheet. Scatter the cooked vegetables over the pastry and loosely fold the pastry edges over to form a rim.
Sprinkle the Parmesan cheese over the vegetables and cook in the oven for 20-30 minutes.